The current-feedback operational amplifier (CFOA) allows us to implement any kind of circuit useful in analogue signal processing applications. However, it has limited performance in implementing ...nonlinear circuits. That way, this investigation highlights the experimental results of implementing a multi-scroll chaotic oscillator by using the commercially available CFOA AD844. The chaotic oscillator is based on saturated nonlinear function (SNLF) series, and we show and discuss its frequency limitations to generate 3- to 10-scrolls from 1 kHz to 100 kHz. Finally, we conclude that the frequency limitations are due to the nonideal characteristics of the CFOA-based SNLF block, imposed by the AD844.
The tribological properties of CrAlN, CrAlYN and CrAlZrN coatings deposited by direct current reactive magnetron sputtering are studied by means of pin-on-disc experiments at room temperature, 300, ...500 and 650°C using alumina balls as counterparts. The influence of the metallic composition (Al, Y and Zr) on the friction, wear properties and oxidation resistance is studied by means of scanning electron microscopy, energy dispersive X-ray analysis and Raman analysis of the contact region after the friction tests. The results obtained allow us to classify the tribological behaviour of the CrAl(Y,Zr)N coatings into three groups according to the nature of the dopant and aluminium content. The sliding wear mechanism is characterized by the formation of an overcoat rich in chromium and aluminium oxides whose particular composition is determined by the initial chemical characteristics of the coating and the testing temperature. The fraction of Cr2O3 becomes more significant as the Al content decreases and the temperature increases. The addition of Y, and particularly Zr, favours the preferential formation of Cr2O3 versus CrO2 leading to a reduction of friction and wear of the counterpart. Conversely, the tribological behaviour of pure CrAlN coatings is characterized by higher friction but lower film wear rates as a result of higher hardness and major presence of aluminium oxides on the coating surface.
•Comparative tribological study at high temperature of CrAlN, CrAlYN and CrAlZrN films•Fraction of Cr2O3 raises as the Al content decreases and the temperature increases.•Zr doping favours lower and steady friction coefficient due to higher Cr2O3 formation.•Sliding wear mechanism becomes predominantly abrasive as the Al content increases.•Excellent tribological performance of CrAlN doped with low Y contents (≈2at.%).
To examine the associations of physical fitness (i.e. cardiorespiratory fitness, muscular strength, and speed/agility) with psychological distress and psychological well-being in overweight/obese ...pre-adolescent children.
110 overweight/obese children (10.0±1.1years old, 61 boys) from the ActiveBrains project (http://profith.ugr.es/activebrains) participated in this cross-sectional study.
Physical fitness was evaluated by the ALPHA battery test. Cardiorespiratory fitness was additionally evaluated by a maximal incremental treadmill. Stress was assessed by the Children’s Daily Stress Inventory, anxiety by the State-Trait Anxiety Inventory, depression by the Children Depression Inventory, positive affect and negative affect by the Positive and Negative Affect Scale for Children, happiness by the Subjective Happiness Scale, optimism by the Life Orientation Test, and self-esteem by the Rosenberg Self-Esteem questionnaire. Linear regression adjusted for sex and peak height velocity was used to examine associations.
Absolute upper-body muscular strength was negatively associated with stress and negative affect (β=−0.246, p=0.047; β=−0.329, p=0.010, respectively). Furthermore, absolute lower-body muscular strength was negatively associated with negative affect (β=−0.301, p=0.029). Cardiorespiratory fitness, expressed by the last completed lap, and relative upper-body muscular strength were positively associated with optimism (β=0.220, p=0.042; β=0.240, p=0.017, respectively). Finally, absolute upper-body muscular strength was positively associated with self-esteem (β=0.362, p=0.003) independently of sex and weight status (p for interactions >0.3), and absolute lower-body muscular strength was also positively associated with self-esteem (β=0.352, p=0.008).
Muscular strength was associated with psychological distress (i.e. stress and negative affect) and psychological well-being (i.e. optimism and self-esteem) as well as cardiorespiratory fitness was associated with optimism. Therefore, increased levels of physical fitness, specifically muscular strength, could have significant benefits for overweight/obese children psychological health.
Nanostructured coatings with variable contents of tungsten carbide (WC) and amorphous carbon (a-C) are prepared by controlling the sputtering power ratio using WC and graphite targets. XRD and TEM/ED ...analysis shows that increasing the C incorporation, the WC nanocrystalline phases evolve from γ-W
2C to β-WC
1
−
x
. Further C enrichment leads to a nanocomposite structure of small WC
1
−
x
crystals dispersed in a-C matrix. The a-C at.% is estimated by XPS analysis and correlated with the observed tribo-mechanical properties. The hardness and friction properties vary from hard/high friction (36–40
GPa;
μ
=
0.6–0.8) to moderate-hard/low friction (16–20
GPa;
μ
∼
0.2) coatings depending on the film composition. The transition point is found for a-C content of 10
at.%. This correlates with a change from nanocrystalline WC to nanocomposite WC
1
−
x
/a-C coatings. The overall study will help to understand the previous literature data and will serve as guide for a tailored synthesis of these WC/a-C nanocomposites.
We present low spectral resolution molecular interferometric observations at 1.2 mm obtained with the Combined Array for Research in Millimetre-wave Astronomy (CARMA) towards the C-rich AGB star ...IRC+10216. We have mapped the emission of several lines of SiS, H13CN, SiO and SiC2 in the ground and first excited vibrational states with a high angular resolution of 0.25 arcsec. These observations have allowed us to partially resolve the emission of the envelope at distances from the star ≲50 stellar radii (R
⋆), where the stellar wind is mainly accelerated. The structure of the molecular emission has been modelled with a 3D radiation transfer code. The emission of line SiS (v = 0, J = 14–13) is best reproduced with a set of maser emitting arcs arranged between 5 and 20R
⋆. The abundance of H13CN with respect to H2 decreases from 8 × 10−7 at 1–5R
⋆ to 3 × 10−7 at 20R
⋆. The SiO observations are explained with an abundance ≲2 × 10−8 in the shell-like region between 1 and 5R
⋆. At this point, the SiO abundance sharply increases up to (2–3) × 10−7. The vibrational temperature of SiO increases by a factor of 2 due north-east between 20 and 50R
⋆. SiC2 is formed at the stellar surface with an abundance of 8 × 10−7 decreasing down to 8 × 10−8 at 20R
⋆ probably due to depletion on to dust grains. Several asymmetries are found in the abundance distributions of H13CN, SiO and SiC2 which define three remarkable directions (north-east, south-southwest, and south-east) in the explored region of the envelope. There are some differences between the redshifted and blueshifted emissions of these molecules suggesting the existence of additional asymmetries in their abundance distributions along the line of sight.
The design of a frequency-shift keying (FSK) modulator based on charge-controlled memductor and operating at high-frequency is presented. Firstly, the behavioral model of a memductor, previously ...reported in the literature, is built at SIMULINK under MATLAB environment. It is demonstrated how the ideal incremental memductance increases and decreases according the width and amplitude of a positive and negative pulse signal, respectively, whereas the ideal decremental memductance increases and decreases according the width and amplitude of a negative and positive pulse signal. Secondly, both incremental and decremental memductances are used to on-line reconfigure the frequency of oscillation of a single-memductor controlled oscillator configured as FSK modulator. Once designed the FSK modulator, it is simulated at HSPICE for forecasting its performance. Afterwards, the FSK modulator is built with off-the-shelf devices and tested in lab. The obtained results not only allows an easy reconfigurability of the FSK modulator, but also demonstrate the viability of the memductor to be used in other applications such as cellular neural networks, controllers, sensors, chaotic systems, relaxation oscillators, nonvolatile memory devices and programmable analog circuits.
The electronic structure of the TiO2 (110)-(1×2) surface has been studied by means of angular resolved ultraviolet photoemission spectroscopy (ARUPS). The valence band dispersion along the high ...symmetry surface directions, 001 and 1–10, has been recorded. The experimental data show no dispersion of the band-gap Ti 3d states. However, the existence of dispersive bands along the 001 direction located at about 7eV below the Fermi level is reported. The existence of two different contributions in the emission from the defects-related state located in the gap of the surface is univocally shown for the first time.
► No dispersion of the Ti 3d states was found on the TiO2(110)-(1×2) surface. ► By UPS two components were identified for the defect-related states of this system. ► One component is due to bulk defects and the other to Ti atoms at the 1×2 surface.
The influence of heating/cycling on MgH2 samples milled together with 2 mol% of Nb2O5 was investigated. X-ray diffraction (XRD) shows a reduction of the Nb2O5 to metallic niobium and a possible ...MgNb203.67 phase, along with an increased formation of MgO compared to a pure MgH2 sample. It was shown that the additive during the heating process is preventing the MgH2 phase from grain growth. Using X-ray photoelectron spectroscopy metallic niobium and niobium oxides were observed emerging to the surface only after cycling. All reported reactions had taken place already during the first cycle. Using annealing experiments at different temperatures, samples of the same composition were generated but with different XRD crystal sizes. These samples showed similar sorption kinetics, which indicates that the prevention of grain growth by the Nb2O5 additive can only have a minor effect on the kinetics for this range of crystal sizes. Since the Nb2O5 is reduced during the heating, a possible catalytic effect has to be due to metallic Nb or those of its oxides with oxygen deficiency, like MgNb203.67, formed during the first cycle. However, other processes like particle size reduction or a decrease of agglomeration by the additive during milling also have to be taken into account.
A series of WC/C nanostructured films with carbon contents ranging from 30 to 70at.% was deposited on M2 steel substrates by magnetron sputtering of WC and graphite targets in argon. Depending on the ...amorphous carbon (a-C) incorporated in the coatings, nanocrystalline coating (formed mainly by WC1−x and W2C phases) or nanocomposite (WC1−x/a-C) were obtained with tunable mechanical and tribological properties. Ultrahardness values of 36–40GPa were measured for the nanocrystalline samples whilst values between 16 and 23GPa were obtained in the nanocomposite ones depending on the a-C content. The tribological properties were studied using a pin-on-disk tester versus steel (100Cr6) balls and 5N of applied load in dry sliding conditions and the failure modes by scratch adhesion tests. Three different zones were identified according to the observed tribological behavior: I (μ>0.8; adhesive wear), II (μ: 0.3–0.6; abrasive wear) and III (μ~0.2; self-lubricated). The wear tracks and the ball scars were observed by scanning electron microscopy (SEM) and Raman spectroscopy in order to elucidate the tribochemical reactions appearing at the contact and to determine the wear mechanism present in each type. A correlation among structure, crystalline phases, a-C content and tribomechanical properties could be established for the series of WC/C coatings and extended to understand the trends observed in the literature for similar coatings.
► Comprehensive overview on the tribomechanical properties of WC/C films by analysis of their structural and chemical features. ► Raman spectroscopy is used to correlate changes occuring on coating surfaces during friction test with the wear mechanism. ► Failure modes by scratch testing as a tool for understanding the deformation processes induced during sliding friction. ► The evaluation of the fraction of free carbon allows to understand and predict the tribological and mechanical behaviour.
All-sky cameras are frequently used to detect cloud cover; however, this work explores the use of these instruments for the more complex purpose of extracting relative sky radiances. An all-sky ...camera (SONA202-NF model) with three colour filters narrower than usual for this kind of cameras is configured to capture raw images at seven exposure times. A detailed camera characterization of the black level, readout noise, hot pixels and linear response is carried out. A methodology is proposed to obtain a linear high dynamic range (HDR) image and its uncertainty, which represents the relative sky radiance (in arbitrary units) maps at three effective wavelengths. The relative sky radiances are extracted from these maps and normalized by dividing every radiance of one channel by the sum of all radiances at this channel. Then, the normalized radiances are compared with the sky radiance measured at different sky points by a sun and sky photometer belonging to the Aerosol Robotic Network (AERONET). The camera radiances correlate with photometer ones except for scattering angles below 10∘, which is probably due to some light reflections on the fisheye lens and camera dome. Camera and photometer wavelengths are not coincident; hence, camera radiances are also compared with sky radiances simulated by a radiative transfer model at the same camera effective wavelengths. This comparison reveals an uncertainty on the normalized camera radiances of about 3.3 %, 4.3 % and 5.3 % for 467, 536 and 605 nm, respectively, if specific quality criteria are applied.
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